Apparatus for controlling pacing of a heart in response to changes in stroke volume

ABSTRACT

The apparatus is used for sensing opening and closing of a tricuspid valve in a heart, for using those sensings to determine stroke volume, and for controlling pacing of a heart relative to changes in stroke volume. The apparatus comprises a pacer, a pacing lead coupled to the pacer and having a lead body, a pressure sensor mounted in the lead body and a pacing electrode, circuit means in the pacer coupled to the sensor for sensing the opening of the tricuspid valve during each heart cycle and for sensing the closing of the tricuspid valve during each heart cycle; means for calculating ejection time from the openings and closings of the tricuspid valve; means for calculating the change in ejection time, ΔET, from calculations of ejection time; means for calculating changes in stroke volume, ΔSV, means for determining the required change in heart rate, ΔR, relative to the change in stroke volume, ΔSV; and means for adjusting the pacing rate of said pacer relative to the required change in heart rate, ΔR.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 885,063 filedJuly 14, 1986, for: METHOD FOR CONTROLLING PACING OF A HEART IN RESPONSETO CHANGES IN STROKE VOLUME, issued to U.S. Pat. No. 4,708,143 on Nov.24, 1987; which is a division of application Ser. No. 632,625 filed July19, 1984, issued to U.S. Pat. No. 4,600,017 on July 15, 1986 for: PACINGLEAD WITH SENSOR.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pacing lead with sensor mounted therein formeasuring the occurrence of a phenomenon in a living organism, and moreparticularly, to a pacing lead having a piezoelectric sensor, the pacinglead being implanted in a living organism whereby the phenomenon actingon the sensor will generate an electric waveform indicative of thephenomenon. The phenomenon sensed is typically contractions of theheart.

2. Description of the Prior Art

Heretofore, various sensors have been developed for sensing phenomenaoccurring in living organisms, and particularly, the human body andheart. For example, cardiac sensors are disclosed in U.S. Pat. Nos.2,634,721; 3,038,465; 3,410,441; 3,811,427 and 3,831,588. These sensorshave utilized various complicated constructions, such as strain gaugesin U.S. Pat. Nos. 2,976,865 and 4,003,370, field effect transistors inU.S. Pat. No. 3,946,724, PN type transducers in U.S. Pat. No. 3,710,781,and signal generating semiconductor devices in U.S. Pat. No. 3,811,427.

Further, it has been experimentally suggested to use piezoelectricsensors for measuring heart beats and blood flow by wrapping a band ofpiezoelectric material around a patient's chest or leg, including thoseof the ferroelectric polymer and polyvinylidene fluoride (PVF₂) types.For example, see "Ferroelectric Polymers and their Application" byMicheal A. Marcus, appearing in Ferroelectronics: 40, 1982, and"Piezoelectric High Polymer Foils as Physiological Mechanic-ElectricEnergy Converters" by E. Hausler, H. Lang and F. J. Schreiner, appearingin IEEE 1980 Bio Medical Group Annual Conference, Frontiers ofEngineering in Health Care.

Further, it is known to implant a piezoelectric device in a livingorganism for other purposes, such as to: power a cardiac or other paceras suggested in U.S. Pat. No. 3,659,615, and control or vary the pacingrate with the implantee's own physical activity as disclosed in U.S.Pat. No. 4,140,132.

It has also been known that under controlled clinical conditions onecan, by replacing a microphone on the chest of a person, measure thevibrations of the heart and obtain graphs of waveforms showing, at aminimum, the opening and closing of the heart valves. See, for example,"The Analysis and Interpretation of the Vibrations of the Heart, as aDiagnostic Tool and Physiological Monitor" by C. M. Agress, M.D. and L.G. Fields appearing in IRE Transactions on Biomedical Electronics, July1961.

As will be described in greater detail hereinafter, it has been foundfrom studies on dogs using a pacing lead having a piezoelectric sensormounted in the distal end portion thereof in accordance with theteachings of the present invention, that graphs of waveforms can beobtained clearly showing the opening and closing of the heart valves.This can be significant since from measurements of opening and closingof the heart valves, one can determine stroke volume and then bymultiplying stroke volume by heart rate, one can determine cardiacoutput.

Also as will be described in greater detail hereinafter, the presentinvention provides an apparatus for controlling pacing of a heartrelative to the changes in stroke volume using the pacing lead having alead body and a pressure sensor mounted in the lead body near the end ofthe pacing lead. With this apparatus, openings and closing of atricuspid valve in a heart are sensed by the sensor and such sensingsare used to determine stroke volume.

Heretofore it has been proposed in Mirowski et al, U.S. Pat. No.3,614,954 to mount a pressure sensing bulb on the outside of a pacinglead for the purpose of sensing pressure. These sensings are used todetermine malfunctions of the heart so that the heart can beautomatically defibrillated by sending electrical pulses to electrodeson the pacing lead from an electronic standby defibrillator electricallycoupled to the pressure sensing bulb.

In the Denniston, III U.S. Pat. No. 3,815,611 an apparatus using apiezoelectric sensor is disclosed for sensing or detecting contractionsof the muscles of living animals.

In the Zacouto U.S. Pat. No. 4,052,991 there is disclosed a method ofstimulating a heart in response to pressure sensings sensed by apressure detector mounted in the intraventricular septum of the heart,as shown in FIG. 19 of this patent.

In the Seo U.S. Pat. No. 4,191,193 there is disclosed a catheterhead-type transducer for measuring pressure in a vessel of a body.

In the Anderson et al. U.S. Pat. No. 4,428,378, the disclosure of whichis incorporated herein by reference, a rate adaptive pacer is disclosedwhich includes an activity sensor mounted within the pacer for detectingthe general activity level of a patient and for then altering the escapeinterval of the pacer between a preset minimum and maximum in responseto the detected activity level of the patient. The pacer includes signalprocessing circuitry which utilizes the sensed activity for controllingthe rate of pacing.

In the Anderson et al. U.S. Pat. No. 4,485,813 there is disclosed inimplantable dynamic pressure transducer system for detecting pressureand other force parameters for use with a pacemaker or other implantedcardiac monitoring and/or treatment device.

Finally, in the Olson U.S. Pat. No. 4,535,774 there is disclosed astroke volume controlled pacer which employs a pacing lead havingelectrodes thereon positioned within a heart chamber for sensing changesin impedance in the heart chamber. Then, the changes in impedance in theheart chamber are used to infer stroke volume. This patent also suggeststhat stroke volume may be inferred by a variety of measurements taken inthe right or left heart and including pressure-time histories ofarterial blood flow, as well as direct flow measurements in the majorblood vessels of the heart.

As will be described in greater detail hereinafter, the apparatus of thepresent invention does not utilize pressure-time histories of arterialblood flow, direct flow measurements in major blood vessels of the heartor changes in impedance within a heart chamber. Instead, the apparatusof the present invention utilizes sensings of the opening and closing ofthe tricuspid valve for determining ejection time and then fromdeterminations of ejection time determining stroke volume and changes instroke volume. The changes in stroke volume are utilized for controllingthe pacing of a heart.

SUMMARY OF THE INVENTION

According to the invention there is provided an apparatus for sensingpressure changes in a heart chamber to determine opening and closing ofa tricuspid valve in a heart, for using those determinations of openingsand closings of the tricuspid valve to determine stroke volume andchanges in stroke volume, and for controlling pacing of a heart relativeto changes in stroke volume, said apparatus comprising: a pacer havingtherein pulse generating circuitry for generating pacing pulses, controlcircuitry for controlling the pulse generating circuitry and a socket; apacing lead having a proximal termination received in said pacer socket,being electrically coupled to said pacer in said socket and having alead body; a pressure sensor mounted in said lead body; a pacingelectrode on said lead body; means for establishing a pacing circuitincluding said pacing electrode, said pulse generating circuitry andsaid control circuitry; said control circuitry including circuit meansin said pacer coupled to said sensor for sensing changes in pressure ina heart chamber to determine the opening of a tricuspid valve duringeach heart cycle and the closing of the tricuspid valve during eachheart cycle; means for calculating ejection time from the openings andclosing of the tricuspid valve; means for calculating the change inejection time, ΔET, from calculations of ejection time; means forcalculating changes in stroke volume, ΔSV from calculations of ejectiontime; means for determining the required change in heart rate, ΔR,relative to the change in stroke volume, ΔSV; and means in said controlcircuitry for adjusting the pacing rate of said pacer relative to therequired change in heart rate, ΔR.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a pacing lead with sensor constructed accordingto the teachings of the present invention.

FIG. 2 is an enlarged cross-sectional fragmentary view of the lead withsensor shown in FIG. 1 and is taken along line 2--2 of FIG. 1.

FIG. 3 is a further enlarged fragmentary view of a portion of FIG. 2.

FIG. 4 is a cross-sectional view of a human heart showing the pacinglead with sensor inserted into the heart in a pacer connected to thelead.

FIG. 5 illustrates an electrocardiogram (EKG) generated by the action ofa dog's heart.

FIG. 6 is a graph of the waveform generated by the sensor in the leadshown in FIG. 1 when the sensor is located just above the apex of theright ventricle, and shows the opening and closing of the semilunarvalves in the heart correlated with the EKG activity shown in FIG. 5.

FIG. 7 is a graph similar to the graph of FIG. 5 of the waveformgenerated by the sensor when it is located just below the tricuspidvalve correlated with the EKG activity shown in FIG. 5.

FIG. 8 is a perspective view of a distal end portion of a pacing leadand shows a sensor therein in the form of a thin film polymerpiezoelectric strip mounted in a spiral or corkscrew configuration inthe pacing lead distal end portion.

FIG. 9 is a perspective view of a distal end portion of a pacing leadand shows a sensor therein in the form of a thin film polymerpiezoelectric elongate strip mounted coaxially of the pacing lead distalend portion.

FIG. 10 is a flow chart of the routine or algorithm carried out by themicroprocessor in the pacer shown in FIG. 4 for controlling the pacer inresponse to changes in stroke volume.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is illustrated therein a unipolar pacing lead8 having a sensor 10 incorporated into a catheter body 12 of the lead 8.The catheter body 12 is of conventional length and size or diameter andis capable of being inserted into an appropriate blood vessel forinsertion to a desired position in a heart. A tip electrode 14 ismounted at distal end 15 of the lead 8. Of course, if desired, bipolarpacing electrodes can be provided on or near the distal end of the lead8.

As is conventional, the pacing tip electrode 14 is connected by a coiledwire conductor 16 (FIG. 2) within the conventional hollow center orlumen 18 (FIG. 2) of the catheter body 12. The coiled wire conductor 16extends from the distal end 15 to a proximal end 20 (FIG. 1) of the lead8 where it is connected to pin electrode 22 adapted to be inserted intoa conventional pacemaker or, if desired, other electronic circuitry.

The sensor 10 is preferably incorporated directly into the body 12 ofthe lead 8, which as is conventional, may be made of a medical gradesilicon rubber, polyurethane, or the like. Preferably, the sensor 10 isin the form of a piezoelectric bimorph 24 located between an outer wall25 of the lead 8 and an inner cylindrical surface 27 defining a wallsurface 27 of the lumen 18. The bimorph 24 as shown in FIG. 3, has apair of ceramic sheets 26 and 28 made of suitable piezoelectricmaterials, such as barium titanate, lead titanate zirconate, leadmetaniobate and/or sodium bismuth titanate. As is conventional, thepiezoelectric sheets 26 and 28 are separated by a shim 30 of materialsuch as brass. Such a suitable bimorph 24 can be obtained fromPiezoelectric Products Inc., or from Vernitron Piezoelectric Division.The bimorph's upper and lower surfaces 32 and 34 are composed of firedon silver or electroless nickel to which a pair of insulated wires 36and 38 are secured, such as by silver soldering, welding, crimping, orwith conductive adhesive. These wires 36 and 38 are incorporated in thebody 12 and extend to the proximal end 22, wherein they are similarlyconnected to a pair of ring or sleeve connectors 40 and 42 (FIG. 1).From there, conventional ring connectors in a socket of a pacer (notshown) which can be of the type disclosed in the Peers-Trevarton U.S.Pat. Nos. 4,458,695 and 4,469,104 the disclosures of which areincorporated herein by reference will connect the sleeves 40 and 42 toappropriate electronic circuitry in the pacer.

The exact placement of the bimorph 24 along the length of the lead 12 isdependent upon what is desired to be monitored. For example, if thesensor 10 is to monitor the activity of the tricuspid valve 50 (FIG. 4)between the right atrium 52 and the right ventricle 54, the bimorph 24would be placed a distance of approximately 7 to 8 centimeters from thedistal end of the lead 8 to be just below the tricuspid valve as shownby sensor 24a in FIG. 4. If, for example, the pressure of blood in theventricle is to be monitored, the bimorph 24 would be placed closer tothe distal end 15, say 1 to 3 centimeters, so that it will be locatedwithin the ventricle 54 and just above the apex or bottom of theventricle 59 as shown by sensor 24b in FIG. 4. Likewise, if the interestwas the pressure of blood in the atrium 52, the bimorph 24 could beplaced even farther from the distal end, say 9 to 11 centimeterstherefrom, so as to be located in the atrium 52.

It is important to note that the bimorph 24 is totally encapsulatedwithin the lead body 12, so that it is isolated from the blood, and yetis still able to sense any pressure changes as a result of the openingand closing of the tricuspid valve 50. This is because the bimorph 24,rather than measuring an accurate absolute pressure, functions somewhatlike a microphone, or more like a sonar pickup, to pick up pressurepulses and waves generated by the opening and closing of the tricuspidvalve 50, and travelling through the blood, through the encapsulatingsilicone rubber to the bimorph 24, where it stresses the same andgenerates an electrical waveform. The encapsulation material is suchthat pressure pulses or waves can travel therethrough and be transmittedto the bimorph, recoverably stressing the same, to generate electricalwaveform signals. Preferably, the wall thickness of the catheter body isless than one millimeter and the thickness of the encapsulation materialon the outer facing surface of the bimorph 24 is less than 0.2millimeter so as to not unduly diminish the pressure pulse or wave to besensed.

The lead 8 with sensor 10 (bimorph 24) lends itself to telemetering ofthe waveform for waveform analysis, and to interpretation analysis andutilization of the waveform for determining cardiac parameters, such ascardiac output.

In FIG. 5 is shown a copy of an electrocardiogram (EKG) 60 generated bythe action of a dog's heart. The waveform 69 is an electrocardiogram ofthe electrical activity of the dog's heart occurring during aventricular contraction.

In FIG. 6 is shown, a waveform 62 generated by and recorded from thebimorph 24b located just above the apex of the ventricle 54.

The waveform 62 shows several important heart functions. In thisrespect, J₂ marks the opening of the semilunar valve and L marks theclosure of the semilunar valve. Also, the H wave of the vibrocardiogramor waveform 62 occurs simultaneously with the onset of left ventricularisometric contraction.

In animal stuides, such a waveform or vibrocardiogram 62 obtained with amicrophone, correlated very well with periods of heart activity measuredmore accurately with other methods. For example, H-J₂ equals the periodof isometric contractions; J₂ -L equals ejection time; H-L equalssystole, L-H equals diastole; and J₁ -J₂ equals rapid ventricularejection.

One of the important periods is the ejection time, J₂ -L since thisperiod can be used to determine stroke volume which is then used todetermine cardiac output so that a doctor can determine theeffectiveness of the ventricular, atrial or dual atrial-ventricularpacing in assisting cardiac output.

In this respect, it has been determined that stroke volume times heartrate equals cardiac output. Here, reference is made to the article"Measurement of Stroke Volume by the Videocardiogram" by Agress et alwhich appeared in the December 1967 issue of Aerospace Magazine. Fromthe studies made by Agress et al, it has been found that:

    Stroke volume (SV)=0.32(J.sub.2 -L)-19.9

Similarly, changes in stroke volume can be defined as follows:

    Δ(SV)=0.30[Δ(J.sub.2 -L)]+0.63

If desired, the isovolumetric contraction time (H-J₂) can be included inthe determination of stroke volume using the videocardiogram although itis not certain that one can obtain a more accurate determination ofstroke volume by utilizing H-J₂ as well as J₂ -L time periods.

Again, stroke volume times heart rate yields cardiac output, a wellestablished indication of heart pumping effectiveness and the pacing ofthe heart to assist heart pumping.

FIG. 7 is a waveform 64 which is generated by sensor 24a located justabove the tricuspid valve 50. Although not known with absolutecertainty, it is believed that O represents opening of the tricuspidvalve and C represents closing of the tricuspid valve.

The sensor 10 of the present invention can be used to measure absoluteand/or relative values of the phenomena being sensed, such as valveopenings and closings, by viewing the resultant waveforms or traces 62or 64 obtained with the bimorphs 24b or 24a located at various positionsin the heart and such waveforms provide useful and valuable information.The comparison between various generated traces provides a physicianwith a powerful tool in analyzing any changes in a patient's condition,e.g., change in ejection time. The primary phenomenon measured in aheart is the change in blood pressure in one of the heart chambers asthe heart contracts and expands.

Also, the sensor 10 of the present invention can be made in other formsthan a piezoelectric bimorph 24. In this respect, the sensor 10 can berealized by a piezoelectric strip 70 constructed of a thin film polymer,e.g. polyvinylidene fluoride (PVF₂) and mounted in a pacing lead distalend portion 72 in a spiral or corkscrew configuration 74 as shown inFIG. 8.

Alternatively, a straight piezoelectric strip 80 constructed of a thinfilm polymer, e.g. polyvinylidene fluoride (PVF₂) can be used for thesensor 10 and mounted in and coaxially of the elongate axis of a pacinglead distal end portion 82 as shown in FIG. 9.

Of course, the sensor 10 of the present invention can be designed formonitoring other cardiac functions besides changes in blood pressure,such as monitoring atrial or ventricular contractions, opening orclosing of other cardiac valves, measuring blood turbulence, or othercardiac activity. Also, the sensor 10 can be incorporated in other thana cardiac lead 8, and could be used to sense phenomena occurring invarious parts of the body, such as in the ventricles of the brain or theurinary bladder.

Also, it will be understood that the waveforms obtained can be analyzedby a microprocessor in a body implanted pacemaker or a pacer, such aspacer 90 with microprocessor 92 shown in FIG. 4, or in an externalsignal processing circuit and the openings and closings of particularvalves, e.g., semilunar valves or tricuspid valves, in the heart can bedetermined and this information can be utilized for controlling thepacing pulses, particularly the rate thereof, supplied to the electrode14 as shown in FIG. 10. A conventional pacing circuit will include theelectrode 14 and an indifferent electrode such as the pacer case 93(FIG. 4) or a ring electrode 94 (FIG. 4) on the lead 81 controlcircuitry in the pacer 90 including the microprocessor 92 andconventional pulse generating circuitry as disclosed in the Purdy U.S.Pat. No. 3,649,367 (anode pole is at the pulse generator--i.e., at thecasing) and the Heilman et al U.S. Pat. No. 4,303,075 (pulse generatorand pairs of electrodes), the disclosures of which are incorporatedherein by reference.

While one preferred embodiment of a pacing lead 8 with a sensor 10 hasbeen illustrated and described above, it is to be understood thatvariations and modifications and equivalent structure can be madewithout departing from the teachings of the present invention.Accordingly, the scope of the invention is only to be limited asnecessitated by the accompanying claims.

I claim:
 1. An apparatus for sensing pressure changes in a heart chamberto determine opening and closing of a tricuspid valve in a heart, forusing those determinations of openings and closings of the tricuspidvalve to determine stroke volume and changes in stroke volume, and forcontrolling pacing of a heart relative to changes in stroke volume, saidapparatus comprising: a pacer having therein pulse generating circuitryfor generating pacing pulses, control circuitry for controlling thepulse generating circuitry and a socket; a pacing lead having a proximaltermination received in said pacer socket, being electrically coupled tosaid pacer in said socket and having a lead body; a pressure sensormounted in said lead body; a pacing electrode on said lead body; meansfor establishing a pacing circuit including said pacing electrode, saidpulse generating circuitry and said control circuitry; said controlcircuitry including circuit means in said pacer coupled to said sensorfor sensing changes in pressure in a heart chamber to determine theopening of a tricuspid valve during each heart cycle and the closing ofthe tricuspid valve during each heart cycle; means for calculatingejection time from the openings and closings of the tricuspid valve;means for calculating the changes in ejection time, ΔET, fromcalculations of ejection time; means for calculating changes in strokevolume, ΔSV from calculations of ejection time; means for determiningthe required change in heart rate, ΔR, relative to the changes in strokevolume, ΔSV; and means in said control circuitry for adjusting thepacing rate of said pacer relative to the required change in heart rate,ΔR.
 2. The apparatus of claim 1 wherein said socket had ring connectorspositioned therein; said lead body is flexible and comprises: agenerally cylindrical outer wall surface, a lumen within and extendingthe length of said lead body, a given wall thickness, a proximal end, aproximal end portion, a distal end, and a distal end portion; saidpacing electrode includes a tip electrode mounted at said distal end ofsaid lead body for pacing a heart muscle; said lead further includes: aterminal pin extending from said proximal end of said lead body; firstand second spaced apart metallic sleeve connectors on said proximal endportion; a pacer wire conductor within said lumen of said lead body andhaving a distal end connected to said tip electrode and a proximal endadapted to be connected to said pacer through said terminal pin; saidsensor comprises a piezoelectric pressure sensing means mounted in saidlead body distal end portion adjacent to said outer wall surface and ata pre-determined distance behind said tip electrode for generating, frominside the heart, a wave-form of heart activity in response to changesin right ventricular blood pressure, said waveform showing openings andclosings of the tricuspid valve in the right ventricle of a heart whensaid lead body distal end portion is received in the right ventricle ofa heart; said lead also has: first and second wire conductors in saidlead body, each wire conductor having a distal end connected to saidpiezoelectric pressure sensor means and a proximal end connected to saidfirst or second sleeve connector and said sleeve connectors beingelectrically isolated from each other and electrically isolated fromsaid terminal pin; and said sleeve connectors received in said socket insaid pacer make contact with said ring connectors positioned in saidsocket.
 3. An apparaus for sensing pressure changes in a heart chamberto determine opening and closing of a tricuspid valve in a heart, forusing those determinations of openings and closings of the tricuspidvalve to determine stroke volume and changes in stroke volume, and forcontrolling pacing of a heart relative to changes in stroke volume, saidapparatus comprising: a pacer having therein pulse generating circuitryfor generating pacing pulses, control circuitry for controlling thepulse generating circuitry therein and a socket, a pacing lead having aproximal termination received in said pacer socket, being electricallycoupled to said pacer in said socket and having a lead body; a pressuresensor mounted in the lead body; a pacing electrode on said lead body;means for establishing a pacing circuit including said pacing electrode,said pulse generating circuitry and said control circuitry; said controlcircuitry including circuit means in said pacer coupled to said sensorfor sensing changes in pressure in a heart chamber to determine theopening of the tricuspid valve during each heart cycle and the closingof the tricuspid valve during each heart cycle; means for calculatingejection time from the openings and closing of the tricuspid valve;means for calculating the changes in ejection time, ΔET, fromdeterminations of ejection time; means for calculating changes in strokevolume, ΔSV from calculations of ejection time, from the formula:

    ΔSV=0.30(ΔET)+0.63;

means for determining the required changes in heart rate, ΔR, relativeto the change in stroke volume, ΔSV; and means in said control circuitryfor adjusting the pacing rate of the pacer relative to the requiredchange in heart rate, ΔR.